This invention concerns the preparation of polymers with low polydispersity and/or controlled molecular weight and architecture by the use of living free radical polymerization initiated by an alkoxyamine or an appropriate nitroxide-initiator combination. It also concerns novel compounds usefull in such polymerizations and methods for their preparation.
Living radical polymerization based on the use of alkoxyamine initiators was invented by Rizzardo et al and is described in U.S. Pat. No. 4,581,429. Recent publications by Georges et al (Trends Polym. Sci., 1994, 2, 66-72), Hawker (J. Am. Chem. Soc., 1994, 116, 11185-11186) and others have described the application of the methodology to the synthesis of narrow polydispersity polystyrenes. The nitroxide component in these latter studies is most often 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or one of its derivatives. We have now discovered the advantages of nitroxide-mediated living free-radical polymerizations employing imidazoline nitroxides (1) as further defined hereafter: ##STR1##
The characteristics of a living polymerization are discussed by Quirk and Lee (Polymer International 27, 359 (1992)) who give the following experimentally observable criteria:
1. Polymerization proceeds until all of the monomer has been consumed. Further addition of monomer results in continued polymerization. PA1 2. The number average molecular weight (or the number average degree of polymerization) is a linear function of conversion. PA1 3. The number of polymer molecules (and active centers) is a constant which is sensibly independent of conversion. PA1 4. The molecular weight can be controlled by the stoichiometry of the reaction. PA1 5. Narrow molecular weight distribution polymers are produced. PA1 6. Block copolymers can be prepared by sequential monomer addition. PA1 7. Chain end-functionalized polymers can be prepared in quantitative yield. PA1 R, R.sup.1, R.sup.2, R.sup.3 are each independently selected from the group consisting of C.sub.1 to C.sub.18 alkyl, substituted C.sub.1 to C.sub.18 alkyl, C.sub.6 to C.sub.18 aryl, C.sub.6 to C.sub.18 substituted aryl; R groups that are in a geminal position with respect to each other can together form a 4-8 membered ring; R groups that are in a cis position with respect to each other can together form a 4-8 membered ring; PA1 X is selected from the group consisting of hydrogen, C.sub.1 to C.sub.18 alkyl, substituted C.sub.1 to C.sub.18 alkyl, C.sub.6 to C.sub.18 aryl, C.sub.6 to C.sub.18 substituted aryl; acyl; X and R can form a 5-8 membered ring; X and R.sup.3 can form a 5-8 membered ring; PA1 M is one or more monomer units selected from the group consisting of styrene, substituted styrene, alkyl acrylate, alkyl methacrylate, substituted alkyl acrylate, substituted alkyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, PA1 N,N-dialkylacrylamide, N,N-dialkylmethacrylamide, isoprene and butadiene; PA1 n is an integer greater than 1; PA1 Y is a residue derived from a species that initiates free radical polymerization or is selected from the group consisting of C.sub.1 to C.sub.18 alkyl, substituted C.sub.1 to C.sub.18 alkyl, C.sub.1 to C.sub.18 alkoxy, substituted Cto C.sub.18 alkoxy, C.sub.6 to C.sub.18 aryl, C.sub.6 to C.sub.18 substituted aryl. C.sub.6 to C.sub.18 aroyloxy, C.sub.6 to C.sub.18 substituted aroyloxy, (C.sub.1 to C.sub.18 alkoxy)carbonyloxy, (C.sub.6 to C.sub.18 aryloxy)carbonyloxy, and sulfate radical anions; PA1 and PA1 all substituents are independently selected from the group that consists of epoxy, hydroxy, C.sub.1 to C.sub.18 alkoxy, acyl, acyloxy, alkoxycarbonyl, aryloxycarbonyl, cyano, silyl, halo, and C.sub.1 to C.sub.18 dialkylamino. PA1 methyl methacrylate, ethyl methacrylate, propyl methacrylate (all isomers), butyl methacrylate (all isomers), 2-ethylhexyl methacrylate, isobomyl methacrylate, methacrylic acid, benzyl methacrylate, phenyl methacrylate, methacrylonitrile, alpha-methylstyrene, methyl acrylate, ethyl acrylate, propyl acrylate (all isomers), butyl acrylate (all isomers), 2-ethylhexyl acrylate, isobornyl acrylate, acrylic acid, benzyl acrylate, phenyl acrylate, acrylonitrile, styrene, functional methacrylates, acrylates and styrenes selected from glycidyl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate (all isomers), hydroxybutyl methacrylate (all isomers), N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, triethyleneglycol methacrylate, itaconic anhydride, itaconic acid, glycidyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate (all isomers), hydroxybutyl acrylate (all isomers), N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate, triethyleneglycol acrylate, methacrylarnide, N-methylacrylamide, N,N-dimethylacrylamide, N-tert-butylmethacrylamide, N-n-butylmethacrylarnide, N-methylolmethacrylamide, N-ethylolmethacrylamide, N-tert-butylacrylamide, N-n-butylacrylamide, N-methylolacrylamide, N-ethylolacrylamide, vinyl benzoic acid (all isomers), diethylaminostyrene (all isomers), alpha-methylvinyl benzoic acid (all isomers), diethylamino alpha-methylstyrene (all isomers). p-vinylbenzene sulfonic acid, p-vinylbenzene sulfonic sodium salt, trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, tributoxysilylpropyl methacrylate, dimethoxymethylsilylpropyl methacrylate, diethoxymethylsilylpropyl methacrylate, dibutoxymethylsilylpropyl methacrylate, diisopropoxymethylsilylpropyl methacrylate, dimethoxysilylpropyl methacrylate, diethoxysilyLpropyl methacrylate, dibutoxysilyipropyl methacrylate, diisopropoxysilylpropyl methacrylate, trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, tributoxysilylpropyl acrylate, dimethoxymethylsilylpropyl acrylate, diethoxymethylsilylpropyl acrylate, dibutoxymethylsilylpropyl acrylate, diisopropoxymethylsilylpropyl acrylate, dimethoxysilylpropyl acrylate, diethoxysilylpropyl acrylate, dibutoxysilylpropyl acrylate, diisopropoxysilylpropyl acrylate, maleic anhydride, N-phenylmaleimide, N-burylmaleimide, butadiene, isoprene, chloroprene. PA1 (i) is at least one monomer M; PA1 (ii) is at least one imidoline nitroxide of the formula ##STR3## PA1 and a source of free radicals Y.cndot.; and PA1 (iii) is at least one alkoxyamine selected from the formula ##STR4## PA1 wherein: PA1 R, R.sup.1, R.sup.2, R.sup.3 are each independently selected from the group consisting of C.sub.1 to C.sub.18 alkyl, substituted C.sub.1 to C.sub.18 alkyl, C.sub.6 to C.sub.18 aryl, C.sub.6 to C.sub.18 substituted aryl; R groups in a geminal position with respect to each other can together form a 4-8 membered ring; and R groups in a cis position with respect to each other can together form a 4-8 membered ring; and PA1 X is selected from the group consisting of C.sub.1 to C.sub.18 alky, substituted C.sub.1 to C.sub.18 alkyl, C.sub.6 to C.sub.18 aryl, C.sub.6 to C.sub.18 substituted aryl; acyl; X and R can form a 5-8 membered ring; and X and R.sup.3 can form a 5-8 membered ring; with the proviso that R, R.sup.1, R.sup.2, R.sup.3 and X are not all methyl. PA1 R, R.sup.1, R.sup.2, R.sup.3 are each independently selected from the group consisting of C.sub.1 to C.sub.18 alkyl, substituted C.sub.1 to C.sub.18 alkyl, C.sub.6 to C.sub.18 aryl, C.sub.6 to C.sub.18 substituted aryl; R groups in a geminal position with respect to each other can together form a 4-8 membered ring, and R groups in a cis position with respect to each other can together form a 4-8 membered ring; PA1 X is selected from the group consisting of hydrogen, C.sub.1 to C.sub.18 alkyl, substituted C.sub.1 to C.sub.18 alkyl, C.sub.6 to C.sub.18 aryl, C.sub.6 to C.sub.18 substituted aryl; acyl; X and R can form a 5-8 membered ring; and X and R.sup.3 can form a 5-8 membered ring; and PA1 Z is a group having at least one carbon atom and the carbon centered radical Z.cndot. is capable of initiating free radical polymerization of the monomer (M).